A fire involves a chemical reaction between oxygen and a fuel that is raised to its ignition temperature by heat. The fire is extinguished by removing oxygen, reducing a temperature of the fire, separating the oxygen and the fuel, or interrupting chemical reactions of the combustion. Halogen-containing agents, such as Halon agents, are chemical agents that have been effectively used to suppress or extinguish fires. These halogen-containing agents generate chemically reactive halogen radicals that interfere with combustion processes in the fire. However, many Halon agents, such as Halon 1211, Halon 1301, and Halon 2402, have been suggested to contribute to the destruction of stratospheric ozone in the atmosphere, which has led many countries to ban their use. Therefore, effective fire fighting replacements for Halon agents are being developed. For instance, fire suppression systems have been recently developed to extinguish fires in enclosed spaces that introduce a flow of inert gas into the enclosed space to extinguish the fire. Some fire suppression systems use a source of compressed gas as the inert gas. However, the compressed gas requires a large storage area, which adds additional bulk and hardware to the fire suppression system.
Other fire suppression systems have utilized a propellant to generate the inert gas. The propellant is ignited to generate the inert gas, which is then used to extinguish the fire. The inert gas typically includes nitrogen, carbon dioxide (CO2), or water. Some propellants used in fire suppression systems produce up to 20% by volume of CO2. While CO2 is a nonflammable gas that effectively extinguishes fires, propellants that generate copious amounts of CO2 cannot be used to extinguish fires in a human-occupied space because CO2 is physiologically harmful. CO2 has an Immediately Harmful to Life or Health (IDLH) value of a concentration of 4% by volume and causes the human breathing rate to quadruple at levels from 4% by volume to 5% by volume, loss of consciousness within minutes at levels from 5% by volume to 10% by volume, and death by asphyxiation with prolonged exposure at these or higher levels. In addition, it is difficult to produce CO2 by combustion without producing significant amounts of carbon monoxide (CO), which has an IDLH of 0.12% by volume (i.e., 1200 parts per million (ppm)). Many propellants also produce other gaseous combustion products, such as ammonia (NH3), which has an IDLH of 300 ppm; nitric oxide (NO), which has an IDLH of 100 ppm; or nitrogen dioxide (NO2), which has an IDLH of 20 ppm. NO and NO2 are collectively referred to herein as nitrogen oxides (“NOx”). CO2, CO, NH3, and NOx are toxic to people and, therefore, producing these gases is undesirable, especially if the fire suppression system is to be used in a human-occupied space. Furthermore, many of these propellants produce particulate matter when they are combusted. The particulate matter may damage sensitive equipment, is potentially an inhalation hazard, irritates the skin and eyes, and forms a hazardous solid waste that must be properly disposed of. In U.S. Pat. No. 6,024,889 to Holland et al., a chemically active fire suppression composition is disclosed that includes an oxidizer, a fuel, and a chemical fire suppressant and produces CO2, nitrogen, and water when combusted. The composition also undesirably produces smoke and particulate matter upon combustion.
Propellants based on sodium azide (NaN3) have also been developed for use in fire suppression systems. While NaN3-based propellants produce nitrogen as a combustion product, the propellants are problematic to produce on a large scale because NaN3 is toxic. In addition, combusting the NaN3 propellant produces corrosive and toxic combustion products, in the form of smoke, that are very difficult to collect or neutralize before the nitrogen is used to extinguish the fire.
A nonazide-based fire suppression system is disclosed in U.S. Pat. No. 5,957,210 to Cohrt et al. In the fire suppression system, ammonia is reacted with atmospheric air or compressed air to produce nitrogen and water vapor. The ammonia and air are reacted in a combustion chamber of a gas turbine to produce combustion gases that are exhausted into a mixing chamber before being introduced into an enclosed space. Water is sprayed into the combustion chamber to cool the combustion gases. The introduction of the combustion gases into the enclosed space reduces its oxygen content and extinguishes the fire.
Other fire suppression systems utilize a combination of compressed gases and propellants. In U.S. Pat. No. 6,016,874 to Bennett, a fire extinguishing system is disclosed that uses compressed inert gas tanks and solid propellant gas generants that produce inert gases. The solid propellant gas generants are either azide- or nonazide-based and produce nitrogen or CO2 as combustion products while argon or CO2 are used as the compressed gases. The inert gases from each of these sources are combined to produce an inert gas having 52% nitrogen, 40% argon, and 8% CO2 that is used to extinguish the fire.
In U.S. Pat. No. 5,449,041 to Galbraith, an apparatus for extinguishing fires is disclosed. The apparatus includes a gas generant and a vaporizable liquid. When ignited, the gas generant produces CO2, nitrogen, or water vapor at an elevated temperature. The hot gases interact with the vaporizable liquid to convert the liquid to a gas, which is used to extinguish the fire.